1. Field of the Invention
The systems and methods of this invention generally related to communications systems. In particular, the systems and methods of this invention relate to providing a variable state length initialization.
2. Description of Related Art
Multicarrier modulation, which is also known as Discrete Multitone Transmission (DMT), transceivers step a through a number of initialization states prior to entering steady-state communication or xe2x80x9cshowtime.xe2x80x9d In particular, these various initialization states include channel discovery, transceiver training, channel analysis, and the like. These various initialization states allow, for example, the determination of transmitter power levels, line characteristics, training of receiver function such as equalizers or echo cancellers, or any other feature necessary to establish communication, or to exchange parameters and settings, between transceivers.
DSL (Digital Subscriber Line) modems use variable length initialization states for ADSL communications. The ITU ADSL Standards G.992.1 and G.992.2, incorporated herein by reference in their entirety, specify operation of conventional ADSL systems. For example, in xe2x80x9cMulti-Company Proposal for Initialization,xe2x80x9d incorporated herein by reference in its entirety, the C-REVERB1 initialization state and the R-REVERB3 initialization state have a variable length. The length of a state is defined as the number of DMT symbols transmitted in that state where DMT symbols are also known as multicarrier symbols. The length of C-REVERB1 is controlled by the ATU-R (ATU-Rxe2x80x94ADSL Transceiver Unit-Remote) and the length of R-REVERB3 is controlled by the ATU-C (ADSL Transceiver Unitxe2x80x94Central Office). In this example, the ATU-C transmitter continues to sends C-REVERB1 until the ATU-C receiver detects R-REVERB2 sent from the ATU-R. Likewise, the ATU-R transmitter continues to send R-REVERB3 until the ATU-R receiver detects C-REVERB2 sent from the ATU-C transmitter. For example, when the ATU-C receiver has received the R-REVERB3 signal for a sufficient amount of time, the ATU-C transmitter sends the C-REVERB2 signal to the ATU-R which once detected by the ATU-R receiver causes the ATU-R transmitter to exit the R-REVERB3 state. Likewise, when the ATU-R receiver has received the C-REVERB1 signal for a sufficient amount of time, the ATU-R transmitter sends the R-REVERB2 signal to the ATU-C which once detected by the ATU-C receiver causes the ATU-C transmitter to exit the R-REVERB3 state.
It is important for the ATU-R receiver and the ATU-C receiver to control the length of the states because the ATU-C receiver uses the R-REVERB3 signals and the ATU-R receiver uses the C-REVERB1 signals to perform adaptive signal processing algorithms such as, for example, equalizer training and frame synchronization. In general, this method of having an ATU receiver control the length of an initialization state is used in the ITU standards for ADSL G.992.2 and G.992.1.
However, at least one problem associated with this method is that it does not provide the ATU transmitter with the ability to control the length of the states. This is problematic, for example, because often the ATU transmitters may use these signals to also perform local adaptive signal processing, adaptive analog processing functions, or the like. For example, the ATU-C transmitter may use the C-REVERB1 signals to train a local, either analog or digital, echo canceller. In this example, it is important that the ATU-C maintain control of the length of the state, since the ATU-C may not have enough time to complete the echo canceller training if it is determined and regulated by the ATU-R.
Accordingly, an exemplary embodiment of this invention allows, for example, both the ATU transmitter and the ATU receiver to have control of the length of one or more initialization states. For example, an ATU transmitter can send information, such as a message, to the ATU receiver prior to entering or during a variable length initialization state. The information can specify, for example, the minimum length of the initialization state as needed by the ATU transmitter. As is done in conventional ADSL modems, the ATU receiver controls the length of the state by sending a pre-defined signal to the other ATU when the ATU receiver wishes to terminate the state.
Using the above example, based on the C-REVERB1 state, prior to entering or during the C-REVERB1 state, the ATU-C would send a message to the ATU-R indicating the minimum length of the state xe2x80x9cMinState.xe2x80x9d For example, the ATU-C could indicate that MinState equals 1000 DMT symbols for C-REVERB1. In this case, the ATU-R would wait at least 1000 DMT symbols before the ATU-R transmitter would send R-REVERB2 to the ATU-C, and thus terminating the CREVERB1 state.
Aspects of the invention relate to multicarrier modulation communications.
Additional aspects of the invention relate to varying the lengths of initialization states in multicarrier communication system.
Additional aspects of the invention relate to ATU-C and ATU-R controlled initialization state lengths.
Aspects of the invention further relate to transmitter controlled initialization state lengths.
Aspects of the invention further relate to receiver controlled initialization state lengths
Aspects of the invention additionally relate to ATU transmitter and/or receiver controlled initialization state lengths.
Aspects of the invention also relate to exchanging information between transceivers defining state lengths.
Aspects of the invention also relate to advancing to a next initialization state based at least on the completion of a variable state length initialization procedure.
These and other features and advantages of this invention are described in, or are apparent from, the following detailed description of the embodiments.